Vehicle wheel alignment system and methodology

ABSTRACT

A hybrid wheel alignment system and methodology use passive targets for a first pair of wheels (e.g. front wheels) and active sensing heads for another pair of wheels (e.g. rear wheels). The active sensing heads combine image sensors for capturing images of the targets with at least one spatial relationship sensor for sensing a relationship between the active sensing heads. One or both of the active sensing heads may include inclinometers or the like, for sensing one or more tilt angles of the respective sensing head. Data from the active sensing heads may be sent to a host computer for processing to derive one or more vehicle measurements, for example, for measurement of parameters useful in wheel alignment applications.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.12/731,751, filed Mar. 25, 2010, which is a Continuation of U.S.application Ser. No. 12/258,942, filed Oct. 27, 2008, now U.S. Pat. No.7,703,213, which is a Continuation of U.S. application Ser. No.11/987,606, filed Dec. 3, 2007, now U.S. Pat. No. 7,458,165, which is aContinuation of U.S. application Ser. No. 11/487,964, filed Jul. 28,2006, now U.S. Pat. No. 7,313,869, the entire contents of each of whichare hereby incorporated by reference.

TECHNICAL FIELD

The present subject matter relates to techniques and equipment forvehicle wheel alignment utilizing a combination of image-processingbased alignment technologies and one or more other alignmenttechnologies.

BACKGROUND

A current conventional vehicle wheel alignment system uses sensors orheads that are attached to the wheels of a vehicle to measure variousangles of the wheels and suspension. These angles are communicated to ahost system, where they are used in the calculation of vehicle alignmentangles. In the standard conventional aligner configuration, fouralignment heads are attached to the wheels of a vehicle. Each sensorhead comprises two horizontal or toe measurement sensors and twovertical or camber/pitch sensors. Each sensor head also containselectronics to support overall sensor data acquisition as well ascommunications with the aligner console, local user input, and localdisplay for status feedback, diagnostics and calibration support. Thefour sensors and electronics as well as the mechanical housing thatmakes up each head necessarily is duplicated four times, as there is onefor each wheel.

In recent years, wheels of motor vehicles have been aligned in someshops using a computer-aided, three-dimensional (3D) machine visionalignment system. In such a system, one or more cameras view targetsattached to the wheels of the vehicle, and a computer in the alignmentsystem analyzes the images of the targets to determine wheel positionand alignment of the vehicle wheels from the wheel position data. Thecomputer typically guides an operator to properly adjust the wheels forprecise alignment, based on calculations obtained from processing of theimage data. A wheel alignment system or aligner of this image processingtype is sometimes called a “3D aligner.” An example of a vehicle wheelaligner using such image processing is the Visualiner 3D or “V3D”,commercially available from John Bean Company, Conway, Ark., a divisionof Snap-on Incorporated.

Conventional non-vision alignment systems, with sensors mounted directlyon the vehicle wheels, are becoming commodity items. The market pricepoint for conventional systems has continued to drop due to competitionand wider acceptance of image processing type, non-wheel mounted sensor,alignment systems. Main stream conventional alignment systems continueto require high accuracy and established features sets, yet lower costtechnology and manufacturing processes are preferred. Unfortunately,these advances may still achieve only an incremental cost improvement.Desired are systems using wheel-mounted sensor heads of a new paradigmthat reduces cost but maintains accuracy and features.

SUMMARY

The teachings herein improve over conventional alignment systems bycombining image processing aligner type targets for one or more of theheads with camera imaging equipment and position/orientation sensors inother wheel heads.

For example, a wheel alignment system may include a pair of passiveheads and a pair of active sensing heads. The passive heads are adaptedfor mounting in association with a first pair of wheels of a vehiclethat is to be measured by operation of the wheel alignment system. Theactive sensing heads are adapted for mounting in association with asecond pair of wheels of the vehicle. Each of the passive heads includesa target, e.g. as may be observed by an image sensor. Each activesensing head includes an image sensor for producing image data, which isexpected to include an image of a passive target when the various headsare mounted on or in association with the respective wheels of thevehicle. The system also includes at least one sensor module associatedwith one of the active sensing heads. The sensor module is used todetermine a spatial relationship between the active sensing heads, whenthe active sensing heads are mounted on wheels of the vehicle. Thesystem also includes a processor. The processor processes image datarelating to observation of the targets as well as relationship data fromthe sensor module. The data processing enables computation of at leastone measurement of the vehicle.

In accord with another aspect of the disclosure, a sensing head for usein a wheel alignment system includes a housing for mounting on a wheelof a vehicle that is to be measured by operation of the wheel alignmentsystem and an image sensor mounted to the housing. The image sensorproduces image data. In a measurement operation, the image datatypically includes an image of a target in association with anotherwheel of the vehicle. The sensing head also includes at least one tiltsensor mounted to the housing for sensing a tilt angle of the activesensing head when the active sensing head is mounted on a wheel of thevehicle. A processor is responsive to the image data, the sensed tiltangle and a relationship to another had mounted on the vehicle. Acommunication interface coupled to the processor allows transmission ofwheel alignment measurement data, from the active sensing head to a userdevice of the wheel alignment system.

A method of taking at least one measurement of a vehicle in accord withprinciples taught herein involves capturing an image of a targetassociated with a first wheel of the vehicle with an image sensor in afirst head mounted in association with a second wheel of the vehicle, toproduce first image data. An image of a target associated with a thirdwheel of the vehicle is captured with an image sensor in a second headmounted in association with a fourth wheel of the vehicle, to producesecond image data. The method further entails measuring relationships ofthe first and second heads relative to at least one reference. The firstand second image data and the reference relationship measurements areprocessed to compute at least one measurement of the vehicle.

Additional advantages and novel features will be set forth in part inthe description which follows, and in part will become apparent to thoseskilled in the art upon examination of the following and theaccompanying drawings or may be learned by production or operation ofthe examples. The advantages of the present teachings may be realizedand attained by practice or use of the methodologies, instrumentalitiesand combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figures depict one or more implementations in accord withthe present teachings, by way of example only, not by way of limitation.In the figures, like reference numerals refer to the same or similarelements.

FIG. 1 diagrammatically illustrates a first arrangement of targets andactive sensing heads in relation to vehicle wheels.

FIGS. 1A and 1B illustrate different types of targets that may be usedon passive heads.

FIG. 2 is a functional block diagram of a hybrid wheel alignment system,with elements thereof mounted to wheels of a subject vehicle (althoughother elements of the vehicle are omitted for convenience).

FIG. 3 is a side view of some of the wheel mounted components of thesystem, with one of the active sensor heads shown in a partialcross-sectional detail view.

FIG. 4 is a side view of one of the active sensor heads useful inexplaining the relationship of the camera axis to the pitch plane of themeasured gravity vector.

FIG. 5 is a rear view of one of the active sensor heads useful inexplaining the relationship of the camera to the camber plane of themeasured gravity vector.

FIG. 6 is a functional block diagram of the components of one of theactive sensor heads.

FIG. 7 diagrammatically illustrates another arrangement of targets andactive sensing heads in relation to vehicle wheels, in this case usingadditional targets and image sensing for measurement of the spatialrelationship between the active heads.

FIG. 8 is a side view of some of the wheel mounted components of thesystem of FIG. 7, with one of the active sensor heads shown in a partialcross-sectional detail view, generally like that of FIG. 3; but whereinthe spatial relationship sensor utilizes another camera.

FIG. 9 is a functional block diagram of the components of the activesensor heads shown in the detail view in FIG. 7.

FIGS. 10 to 18 diagrammatically illustrate a series of alternativearrangements, having various heads/targets associated with differentcombinations of the vehicle wheels and using various differentconfigurations or equipment for spatial relationship sensing.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant teachings. However, it should be apparent to those skilledin the art that the present teachings may be practiced without suchdetails. In other instances, well known methods, procedures, components,and circuitry have been described at a relatively high-level, withoutdetail, in order to avoid unnecessarily obscuring aspects of the presentteachings.

The examples shown in the various drawings provide relatively low costalignment systems. The exemplary systems are “hybrid” in nature in thatthey combine aspects of image processing with one or more other types ofmeasurement technologies. Such a hybrid system uses visible targets,e.g. on passive heads, for two wheels of a vehicle under test, and thesystem uses a combination of optical imaging sensors (e.g. cameras) andother alignment sensors in active sensing heads that attach to two otherwheels of the vehicle. The passive heads are substantially cheaper tomanufacture than heads used in conventional alignment systems. The costof the active sensing heads may be generally comparable to the cost oftwo heads of a conventional wheel alignment system.

Measuring the position and orientation of the front wheels of thevehicle using imaging technology offers additional advantages, includingthe ability to derive measurements associated with image processingbased wheel alignment that are not normally available in a low costsystem. These additional measurements may include scrub radius, (U.S.Pat. No. 6,532,062), roll radius (U.S. Pat. No. 6,237,234), and castertrail (U.S. Pat. No. 6,661,751).

Reference now is made in detail to the examples illustrated in theaccompanying drawings and discussed below.

FIG. 1 depicts a first arrangement of targets and active sensing headsin relation to wheels of a vehicle 20 that is under test, e.g. tomeasure one or more wheel alignment parameters. Except for the wheels,elements of the vehicle are omitted for ease of illustration.

The wheel alignment system includes a pair of passive heads 21 and 23mounted on respective wheels 22 and 24 of the vehicle, which are frontsteering wheels in this first example. The active sensing heads 25 and27 are adapted for mounting in association with other respective wheels26 and 28 of the vehicle, in this case the rear wheels. Each activesensing head includes an image sensor 29 or 31 for producing image data,which is expected to include an image of a passive target when thevarious heads are mounted to the respective wheels of the vehicle 20. Inthis first example, the image sensors 29 and 31 in the active sensingheads 25 and 27 are two dimensional (2D) imaging devices, e.g. cameras.

The heads 21 and 23 are passive in that they include targets but do notinclude any sensing elements. Each of the passive heads 21 and 23includes a target of a type that may be observed by one of the imagesensors 29 or 31 in the active heads 25 and 27. A target on a passivehead 21 or 23, for image sensing by a sensor on another head, may beactive or passive. An active target, such as a light emitting diode(LED), is a source driven by power to emit energy (e.g. IR or visiblelight) that may be detected by a sensor. A passive target is an elementthat is not driven by power and does not emit energy for detection by asensor. Assuming an image sensor in head 25 or 27, a passive targetwould be an object that reflects (or does not reflect) light or otherenergy in a manner detectable by the respective image sensor. In theexample, although the targets could comprise one or more light emittingelements, the targets comprise light and dark regions that can bedetected when illuminated by other sources and imaged by cameras or thelike in the active sensing heads 25 and 27.

A first example of a target that can be used on either of the passivewheel heads 21 is illustrated in FIG. 1A. In this first example, thetarget is rectangular. A second example of a target that can be used oneither of the passive wheel heads 21 is illustrated in FIG. 1B. In thissecond example, the target is circular. In each case, the targetconsists of a flat plate with a pattern of differently sized circlesmarked on or mounted on the surface of the plate in a pre-determinedformat and pattern. Although specific patterns are shown FIGS. 1A and1B, it will be evident that a large number of different patterns can beused on each target. For example, a larger or smaller number of dots maybe included and other sizes and shapes can be used for the dots. Asanother example, multifaceted plates or objects can also be used for thetargets. Many examples utilize a number of retro-reflective elementsarranged to form each target. For further information, attention isdirected to U.S. Pat. No. 5,724,743 to Jackson.

The system also includes a spatial relationship sensor associated withat least one of the active sensing heads 25 or 27. The spatialrelationship sensor enables measurement of the spatial relationshipbetween the active sensing heads 25 and 27 when the active sensing headsare mounted on wheels of the vehicle. In general, spatial relationshipsensors may measure relative position and/or orientation, depending onthe type of sensor used. A positional measurement refers to the relativeposition of the measured item from the perspective or in the coordinatesystem of the measuring device. Measurement of position generally uses astandard coordinate system such as Cartesian coordinates or polarcoordinates. Orientation may be derived from a three-dimensionalposition measurement, or orientation may be measured independently ofposition. Orientation relates to the rotational position of the measureddevice with respect to the measuring device expressed in a standardcoordinate system. Orientation is generally expressed in rotationalangles in three orthogonal reference planes.

It will be readily apparent to someone skilled in the art that the wheelalignment systems discussed herein may be implemented with variousdifferent types of spatial relationship sensors. In this first example,the system uses two conventional (1D) angle sensors 33 and 35 to measurethe relative angles of the active sensing heads 25 and 27, in the toeplane.

The active heads 25 and 27 also contain gravity sensors or the like tomeasure tilt, typically camber and pitch, of the head. In this firstexample, the head 25 includes one or more tilt sensors 37; and the head27 includes one or more tilt sensors 39.

As shown in a more detailed example later (regarding FIG. 2), the systemalso includes a computer. The computer processes image data relating toobservation of the targets and tilt data, from the active sensing heads.The computer also processes spatial relationship data from the at leastone spatial relationship sensor. The data processing enables computationof at least one measurement of the vehicle.

Measurement using image processing techniques is fundamentally differentthan using conventional angle measurement technology in a wheelalignment system. Although basic image processing techniques are knownto those skilled in the art, a brief description is presented forclarity. The image of a body varies according to the perspective fromwhich such body is viewed and the variation in the image is directlyrelated to and determinable from the perspective angle of the view pathalong which the body is viewed. Furthermore it is known that it ispossible to determine the perspective angles at which an object isviewed merely by relating the perspective image of that object with atrue non-perspective image thereof. Conversely put, it is possible todetermine the angles at which an object is orientated to a view path (ora plane perpendicular thereto) by comparing a perspective image of anobject with a non-perspective image thereof.

In practice, a mathematical representation, or data corresponding to atrue image (i.e. an image taken by viewing the target perpendicularly toits primary plane) and the dimensions of the target are preprogrammedinto the memory of the computer so that, during the alignment process,the computer has a reference image to which the viewed perspectiveimages of the targets can be compared.

The way that the computer calculates the orientation of the target is toidentify certain geometric characteristics on the target, takeperspective measurements of these and compare these measurements withthe true image previously preprogrammed into the memory of the computer.

Furthermore, as the true dimensions of the target are preprogrammed intothe memory of the computer, the method and apparatus of this inventioncan be used to determine the exact position of the target inthree-dimensional space. This can be done by firstly determining theperspective image of certain of the elements of the pattern on thetarget (for example, the distances between circles) and comparing thedimensions of this image to the true dimensions of those elements. Thiswill yield the distance that the element and, accordingly, the target isfrom the image sensor.

For the wheel alignment system discussed herein, the image sensor in theactive head views a target attached to a wheel and produces image datawhich describes a perspective image of the target. The computercorrelates the perspective image data for the targets with the trueshape of the target. In so doing, the computer relates the dimensions ofcertain known geometric elements of the target with the dimensions ofcorresponding elements in the perspective image and by performingcertain trigonometric calculations (or by any other suitablemathematical or numerical methods), calculates the alignment of thewheel of the vehicle. The computer can also calculate thethree-dimensional position and orientation of the axis of rotation ofthe wheel (wheel axis) associated with the passive target.

For additional information regarding measurement based on processing ofimages of targets, attention again is directed to U.S. Pat. No.5,724,743 to Jackson.

FIG. 2 depicts a more comprehensive example of a low cost hybrid wheelalignment system 50 as well as four wheels 41, 43, 45 and 47 of avehicle (otherwise not shown, for simplicity). The system 50 includesfour heads 51, 53, 55 and 57 for mounting on or otherwise in associationwith the wheels 41, 43, 45 and 47 as shown stylistically in the drawing.A variety of different types of mounting devices may be used. In thisexample, the passive heads 51 and 53 are mounted on the front wheels 41and 43, and the front heads 51 and 53 use retro-reflective targets. Whenmounted on the wheels as shown, the retro-reflective targets facerearward, so as to be observable by the image sensors in the respectiveactive sensing heads. The retro-reflective targets may be similar tothose used in three-dimensional (3D) machine vision alignment systems.The heads 55 and 57 mounted on the rear wheels 45 and 47 are activesensing heads, in that they include image sensing elements. In thisexample, the heads 55 and 57 further include tilt and spatialrelationship sensing elements, as discussed below, for obtaininginformation for processing by a host computer system 100 of the wheelalignment system 50.

An imaging sensor, similar to the V3D camera, is positioned in each ofrear heads. The optical axis of each such camera faces forward along thetrack of the vehicle, in order to measure the position and orientationof the targets attached to the front wheels. The cameras need not bedirectly on the track of the vehicle wheels, that is to say on the rollline of the wheels. The cameras need only to face alongside the wheeltrack sufficiently to view and capture images of the targets on thepassive heads 51, 53 associated with the front wheels. In the example,the active sensing head 55 includes an image sensing module or the likecontaining an image sensor in the form of a camera 61 facing forwardalong the track of the left wheels. When so mounted, the field of viewof the camera 61 includes the target portion of the passive head 51mounted on the left front wheel 41. Similarly, the active sensing head57 includes an image sensing module or the like containing an imagesensor in the form of a camera 63 facing forward along the track of theright wheels. When so mounted, the field of view of the camera 63includes the target portion of the passive head 53 mounted on the rightfront wheel 43.

One or more sensors are attached to the rear heads 55, 57 and positionedto measure a spatial relationship between the two active sensing heads.A variety of available sensing technologies may be used, and twoexamples are discussed, later. In the example illustrated in FIG. 2, theactive sensing head 55 includes a sensor 65; and the active sensing head57 includes a sensor 67. The sensors 65 and 67 in this application areused for sensing the relative angular relationship between the activesensing heads 55 and 57, whereas the image signals from the cameras 61and 64 are processed to compute regular front wheel alignmentparameters, such as camber and toe.

Each rear head 55 or 57 also incorporates one or more inclinometers,which are used as tilt sensors to measure the relative camber and pitchangles of each rear head to gravity. These inclinometers, for example,may comprise MEMS type devices designed to be integral to the trackcamera printed circuit board.

FIG. 3 is a side view of some of the wheel mounted components of thesystem. This left side view shows the left front head 51, with itspassive target, attached to the left front wheel 41. The side view alsoshows the left rear active sensing head 55, attached to the left rearwheel 45. FIG. 3 also provides an enlarged detail view, partially incross section, of elements of the active sensing head 55.

As shown, the head 55 comprises a housing 71. Hardware for mounting thehousing to the wheel is omitted for clarity. The housing 71 contains theforward facing track camera 61. In this example, the spatialrelationship sensor 65 uses a beam angle detection technology, discussedlater with regard to FIG. 6, although other types of sensors may beused. The housing also contains a keypad 74 for user activation of thehead 55 and a printed circuit board 75 containing the data processingelectronics for processing the data from the camera(s) and other sensorsand communications with the host computer. For purpose of forming thesensing head of a hybrid system, the board 75 also supports a pitch tiltsensor 77 and a camber tilt sensor 79. Although shown separately, thetwo tilt sensors 77, 79 may be elements of a single inclinometer module.The sensors 77, 79 communicate inclination readings to a processor onthe board 75, for transmission with the camera data to the host computersystem 100.

FIGS. 4 and 5 are somewhat stylized illustrations of the active sensinghead 55, in side and rear views, which illustrate the relationship ofthe axes measured by the tilt sensors to the other elements. It isassumed for discussion here that the tilt sensors 77-79 are elements ofa single MEMS inclinometer. The inclinometer determines the gravityvector with respect to the pitch plane (FIG. 4) and the gravity vectorwith respect to the camber plane (FIG. 5). Similar measurements, ofcourse, are taken for the other active sensing head 57 (FIG. 2). In thisway, each head's orientation to gravity can be processed to relate eachtrack facing camera's optical axis to gravity (FIGS. 4 and 5). In thisway the relationship of each front target to gravity can also bemeasured by processing of the image data and the gravity vector data.

FIG. 6 is a functional block diagram of the elements of one of theactive sensing heads, in this case the head 55, although the elements ofthe head 57 will be generally similar in this first example.

As discussed above, the active sensing head 55 includes an image sensingmodule 81 or the like containing an image sensor in the form of thetrack camera 61 which in use will face forward along the track of theleft wheels to allow that camera to obtain images containing the targetof the passive head 51 (see also FIG. 2). The track facing image sensormodule 81, illustrated in FIG. 6, includes an LED array 83, serving asan illuminator, to emit light for desired illumination of the target onthe head 51 mounted to the vehicle wheel 41 on the same side of thevehicle. The camera 61 is a digital camera that senses the image for thewheel alignment application. In operation, the camera 61 generates avalue of each image pixel based on analog intensity of the sensed lightat the point in the image corresponding to the pixel. The value isdigitized and read out to circuitry on the main printed circuit board75. The value may be digitized either on or off of the camera sensorchip.

In this implementation, the spatial relationship sensor module 65comprises an IR LED 85, an aperture 86 and a linear image sensor 87 suchas a charge-coupled device (CCD) or CMOS unit. The IR LED 85 projects abeam of light toward a similar toe sensor module in the opposite head57. In a similar manner, the opposite head 57 includes an IR LED thatprojects a beam of light toward head 55.

The IR light/radiation from the IR LED of the opposing head 57 is sensedby the linear image sensor 87, via the aperture 86. The precise point onthe sensor 87 at which the IR light from the other head is detectedindicates the relative angle of incidence of the light from the oppositehead at the sensor 87 in the head 55. In a similar fashion, the IRlight/radiation from the IR LED 85 of the head 55 is sensed by thelinear image sensor, via the aperture in the opposite head 57; theprecise point on the opposite linear image sensor at which the IR lightfrom the LED 85 is detected indicates the relative angle of incidence ofthe light from the head 55 at the linear sensor in head 57. Processingof the angle detection data from the two linear sensors enablesdetermination of the angular relationship between the optical cameraaxes of the cameras 61 and 63 in the two active sensing heads.

The circuit board 75 includes a digital signal processor (DSP) or otherimage processor type circuit and an associated data/program memory 91.In operation, each camera 61, 63 supplies digital image data to theimage processing circuitry 89. As shown, the active sensing head 55 alsoincludes the camber tilt sensor 79 and the pitch tilt sensor 77. Theseinclinometer elements supply the gravity angle measurements (seediscussion of FIGS. 4 and 5) to the processor 89. The image processingcircuitry 89 performs one or more operations on the data and suppliesthe data to a communications interface 93, for transmission to the hostcomputer system 100.

The image processing operations of the circuit 89 may involve formattingvarious data for communication. Alternatively, the processor 89 mayimplement some degree of pre-processing before transmission to the hostcomputer system 100. With regard to the image data, image pre-processingmay include gradient computation, background subtraction and/orrun-length encoding or other data compression (see e.g. U.S. Pat. No.6,871,409 by Robb et al.). The processor 89 may also process the imagedata to some degree in response to the tilt data from the tilt sensors77, 79 and/or the spatial relationship measurement data. Alternatively,the tilt and cross position data may simply be forwarded to the hostcomputer for use in further processing of the image data.

The processor 89 in one of the active heads may be configured to receivedata from the other head and perform wheel alignment parametercomputations, internally, and then send only the vehicle measurementresults to the host computer system 100. Moreover, processor 89 in oneof the active heads may be configured to calculate all alignment valuesand also generate the user interface. In this case the active head mayact as a web server to serve web pages that implement the user interfacefor the wheel alignment system, and the host computer may consist of anygeneral purpose computer with a web browser and no wheel alignmentspecific software. However, to minimize cost, the major portion of thedata processing may be performed at the host, in which case theprocessing by (and thus complexity of) the DSP/processing circuit 89 maybe kept to a minimum.

The processor 89 or another controller (not separately shown) on theboard 75 also provides control over operations of the active sensinghead 55. For example, the control element (processor 89 or othercontroller) will control the timing and intensity of emissions by theLED array 83 and the IR LED 85 as well as the timing and possibly otheroperational parameters of the camera 81 and the linear image sensor 87.The active sensing head 55 also includes a keypad 74 for user activationof the head 55, and the processor 89 or other controller will sense andrespond to inputs via the keypad 74.

The computer communication interface 93 provides two-way datacommunications for the components of the active sensing head 55 with thehost computer 100 (FIG. 2) and in some configurations between the activeheads. The communications interface 93 conforms to an appropriate dataprotocol standard and provides a coupling to a desired physical media,to enable data communication to and from the host computer 100 atdesired speeds and in a manner desired for the particular installation.For example, the host communications interface may be a USB interfacewith a USB connector for cable connection to a matching interface in thehost computer 100. Those skilled in the art will recognize that otherdata communications interfaces may be used in wheel alignment systems,such as Ethernet, RS-232, RS-422, RS-485, WIFI or wireless Ethernet,Zigbee, Bluetooth, UWB (Ultra-Wideband), IrDA, or any other suitablenarrowband or broadband data communication technology.

Electronic circuits on board 75 as well as elements of image sensingmodule 81 and spatial relationship sensor module 85 receive power from asupply 94. Any conventional supply of an adequate level of voltage andcurrent may be used. If system 50 uses cables, the supply may run from aconventional AC power grid or receive power over USB or Ethernetcabling. If heads 55 and 57 are wireless, the power supply may utilizebattery power, either from rechargeable or disposable batteries.Alternatively, power storage media for wireless heads may consists ofsuper-capacitors.

Returning to FIG. 2, host computer system 100 processes data from theactive sensing heads 55, 57 and provides the user interface for thesystem 50. As noted above, data processing could be done in a DSP or thelike in one or more of the active sensing heads 55, 57. However, tominimize the cost of the heads 55 and 57, main processing power may beprovided by the host computer system 100 or similar data processingequipment. In the example, the system 100 may be implemented by adesktop type personal computer (PC) or other computer device such as anotebook computer, UMPC (ultra mobile PC), or similar device. A clientserver arrangement also could be used, in which case the server wouldperform the host processing and one of the active heads or another userdevice would act as a client to provide the user interface. Althoughthose skilled in advanced wheel alignment technologies will be familiarwith the components, programming and operation of various suitablecomputer systems, it may help to provide a brief example.

Computer system 100 includes a central processing unit (CPU) 101 andassociated elements for providing a user interface. The CPU section 101includes a bus 102 or other communication mechanism for communicatinginformation, and a processor 104 coupled with the bus 102 for processinginformation. Computer system 100 also includes a main memory 106, suchas a random access memory (RAM) or other dynamic storage device, coupledto bus 102 for storing information and instructions to be executed byprocessor 104. Main memory 106 also may be used for storing temporaryvariables or other intermediate information during execution ofinstructions by processor 104. Computer system 100 further includes aread only memory (ROM) 108 or other static storage device coupled to bus102 for storing static information and instructions for processor 104. Astorage device 110, such as a magnetic disk or optical disk, is providedand coupled to bus 102 for storing information and instructions.Although only one is shown, many computer systems include two or morestorage devices 110.

The illustrated embodiment of the computer system 100 also provides alocal user interface, for example, so that the system appears as apersonal computer or workstation as might be used in a wheel alignmentbay or an auto service shop. The computer system 100 may be coupled viabus 102 to a display 112, such as a cathode ray tube (CRT) or flat paneldisplay, for displaying information to a computer user. An input device114, including alphanumeric and other keys, is coupled to bus 102 forcommunicating information and command selections to processor 104.Another type of user input device is cursor control 116, such as amouse, a trackball, or cursor direction keys for communicating directioninformation and command selections to processor 104, which the CPU 101in turn uses for controlling cursor movement on display 112. The cursorinput device 116 typically has two degrees of freedom in two axes, afirst axis (e.g., x) and a second axis (e.g., y), that allows the deviceto specify positions in a plane. The couplings between the userinterface elements 112-116 and the CPU 101 may be wired or may useoptical or radio frequency wireless communication technologies.

The CPU 101 also includes one or more input/output interfaces forcommunications, shown by way of example as an interface 118 for two-waydata communications with the active sensing heads 55 and 57. For purposeof the wheel alignment application, the interface 118 enables the CPU toreceive image data, spatial relationship measurement data and tilt datafrom the active sensing heads 55 and 57. Typically the interface 118also allows the host computer system 100 to send operational commandsand possibly software downloads to the active sensing heads 55 and 57.For example, the communications interface 118 may be a USB interfacewith a USB connector for cable connection to matching interfaces 93 inthe active sensing heads 55, 57. Those skilled in the art will recognizethat other data communications interfaces may be used in wheel alignmentsystems such as Ethernet, RS-232, RS-422, RS-485, WIFI or wirelessEthernet, Zigbee, Bluetooth, UWB. IrDA or any other suitable narrowbandor broadband data communication technology.

Although not shown another communication interface may providecommunication via a network, if desired. Such an additional interfacemay be a modem, an Ethernet card or any other appropriate datacommunications device. The physical links to and from the additionalcommunication interface(s) may be optical, wired, or wireless.

Although the computer 100 may serve other purposes in the shop, thealignment system 50 uses the computer system 100 for processing datafrom the heads 55, 57 to derive desired alignment measurements from thedata provided by the heads, and to provide the user interface for thesystem 50. The computer system 100 typically runs a variety ofapplications programs and stores data, enabling one or more interactionsvia the user interface, provided through elements such as 112-116 toimplement the desired processing. For wheel alignment applications, theprogramming will include appropriate code to process the data receivedfrom the particular implementation of the heads 55, 57, includingcomputations to derive desired vehicle wheel alignment measurementparameters from the various data from the heads 55 and 57. The hostcomputer 100 will typically run a general purpose operating system andan application or shell specifically adapted to perform the alignmentrelated data processing and provide the user interface for input andoutput of desired information for alignment measurements and relatedservices. Since it is a general purpose system, the system 100 may runany one or more of a wide range of other desirable application programs.

The components contained in the computer system 100 are those typicallyfound in general purpose computer systems used as servers, workstations,personal computers, network terminals, and the like. In fact, thesecomponents are intended to represent a broad category of such computercomponents that are well known in the art.

At various times, the relevant programming for the wheel alignmentapplication may reside on one or more of several different media. Forexample, some or all of the programming may be stored on a hard disk orother type of storage device 110 and loaded into the Main Memory 106 inthe CPU 101 for execution by the processor 104. The programming also mayreside on or be transported by other media for uploading into the system100, to essentially install and/or upgrade the programming thereof.Hence, at different times all or portions of the executable code or datafor any or all of the software elements may reside in physical media orbe carried by electromagnetic media or be transported via a variety ofdifferent media to program the particular system and/or the electronicsof the active sensing heads 55, 57. As used herein, terms such ascomputer or machine “readable medium” therefore refer to any medium thatparticipates in providing instructions to a processor for execution.Such a medium may take many forms, including but not limited to,non-volatile media, volatile media, and transmission media (e.g. wires,fibers or the like) as well as signals of various types that may carrydata or instructions between systems or between system components.

Runout compensation for the heads could be performed as with traditionalconventional alignment heads by elevating the rear wheels and using thecamber sensors to measure the runout vector then elevating the frontwheels and using cameras to image the targets as they rotate about thefront wheel's axis. An alternate method would be to avoid elevating thewheels by rolling the vehicle along the lift and performing the runoutmeasurements on the heads with the inclinometers as the track camerasimage the front targets as well as fixed targets on the lift, vehicle orother stationary object in order to establish the fixed coordinatesystem.

As noted, the rear heads 55, 57 incorporate inclinometer type tiltsensors to measure the relative camber and pitch angles of each rearhead to gravity. Once runout is taken and the inclinometer angle valuesare measured, each head's orientation to gravity could be processed torelate each track facing camera's optical axis to gravity. Using therelationship of the track facing camera to gravity and the measuredrelationship of the front target to the track facing camera, therelationship of the front target to gravity can be calculated. A spatialrelationship is measured by the sensors 65 and 67, to determine thespatial relationship between the track cameras 61 and 63.

Front toe, caster, and SA1 would be measured using techniques similar tothose embodied in an imaging aligner, such as the V3D aligner. The rearthrust angle, each rear individual toe, and the horizontal angularrelationship of the track cameras to each other, would be derived fromthe measurements obtained by the rear spatial relationship sensors. Theinclinometers would relate each track camera to each other through thecommon gravity vector references. With the track cameras effectivelyrelated to each other along the axis of the rear thrust line, each fronttarget's location and orientation can be determined in a coordinatesystem that is directly related to the thrust angle and to gravity.

Calibration may be performed by mounting each rear head on a straightcalibration bar in much the same way that the current conventional headsare calibrated. The bar is first rotated to compensate for runout. Thezero offset of the rear spatial relationship sensors can then be set andby leveling the calibration bar, each camber sensor zero offset can beset. The pitch zero offset is set by leveling the head with a precisionlevel bubble and recording the pitch inclinometer value. Enhanced cameracalibration may be achieved by adding another calibration bar adapted tomount the front targets in view of the track cameras (see e.g. U.S.Patent Application Publication No. 2004/0244463 by James Dale, Jr.).After the initial calibration above is performed, the track camerasmeasure the orientation of the front targets as the targets and bar arerotated about the axis of the front calibration bar. The relationship ofone camera to the other may be calculated and thus the relationship ofeach camera to the rear spatial relationship checked or calibrated. Byleveling the front target calibration bar, the fixed relationship ofeach track camera to the local inclinometers may also be checked. Thisredundant check could possibly constitute an ISO check for customersthat require measurement accuracy traceability.

In addition, small targets may be affixed to each front turntableallowing for an additional measurement or cross check of turn angle.

The V3D ride height pointer may also be used to measure front bodypoints for ride height or other body index purposes.

It will be readily apparent to someone skilled in the art that the wheelalignment systems discussed herein may be implemented with variousdifferent types of spatial relationship sensors. An image sensor is onetype of spatial relationship sensor. An image sensor may consist of acamera with a two dimensional array of sensing elements that producesdata representative of an image expected to contain a target within thefield of view of the sensor. The data from the image sensor can beprocessed to determine position and orientation information related tothe viewed target and thus the head, wheel or other object with whichthe target is associated. An example of a prior art image sensor is thecamera used in the Visualiner 3D commercially available from John BeanCompany, Conway, AR, a division of Snap-on Incorporated. An angle sensoris another type of applicable spatial relationship sensor. An anglesensor produces data representing the angle from the sensor relative toa point. Various types of angle sensors are generally known. One exampleof an angle sensor is the linear CCD sensor as used in the Visualineravailable from John Bean Company.

Hence, it may be helpful now to consider an example in which theaperture and linear image sensor style spatial relationship sensingarrangement described above relative to FIGS. 3 and 6 is replaced by animaging type camera similar to the track camera. FIGS. 7 to 9 areviews/diagrams similar to those of FIGS. 1, 3 and 6, except that theillustrations of this second implementation show such an alternatetechnology using a target and image sensor for the spatial relationshipsensing function. Wheels and elements similar to those of theimplementation of FIGS. 1, 3 and 6 are similarly numbered and areconstructed and operate in essentially the same fashion as discussedabove. This example uses passive two-dimensional targets 51 and 53 onthe front wheels 41 and 43; and it uses active heads 55′ and 57′ on therear wheels for the measurements alongside the vehicle tracks, much asin the example of FIG. 1. The rear active sensing heads use cameras 61,63 or similar 2D image sensors to obtain images of the targets on thefront heads 51, 53 and determine the relative positions and orientationsof the targets with respect to the active heads, as discussed in detailabove relative to FIG. 2. However, the spatial relationship of the twoactive heads 55′, 57′ is determined by at least one 2D image sensor 97,which obtains images of a 2D target 67′ mounted on the opposite activehead. In this example, the active head 57′ has an associated target 67′similar to one of the targets on head 51 and 53, but the head 57′ doesnot include a sensor for the spatial relationship measurement function.The active sensing head 55′ uses an image processing type approach tothe spatial relationship measurement across the rear of the vehiclebased on imaging the target 67′. The image sensor 97 typically would besimilar to the cameras or the like used as 2D image sensors in theexample of FIG. 2.

As shown in more detail in FIGS. 8 and 9, the spatial relationshipsensor 95 uses an image sensing module similar to the track facing imagesensor module 81. The spatial relationship image sensing module 95includes a digital camera 97 and an LED array 99. The LED array 99serves as an illuminator. For the spatial relationship sensingapplication, the LED array 99 produces infrared (IR) illumination. Theother rear head 57′ includes an IR sensitive retro-reflective target 67′(FIG. 7) to be illuminated by the LED array 99, which in turn is sensedby the camera 97.

The spatial relationship camera 97 images the target 67′ positioned onthe companion head (across the rear of the vehicle) in place of theother spatial relationship sensor. Both cameras 61 and 97 could share acommon processing board in the one head while the other head may simplyuse a single camera (for track) and a target (for cross). Processing ofthe target image obtained by camera 97 can compute the angular spatialrelationship between the rear heads, in much the same way as the imagesfrom the active head cameras were processed to determine relative angleand/or position of the wheel mounted targets in the examples of FIGS. 1and 2. Rather than measuring a spatial relationship angle as in theprevious example, the image sensing module and associated imageprocessing measures the 3D spatial relationship of the target on theopposite active head. For additional information regarding measurementbased on processing of images of targets, attention again is directed toU.S. Pat. No. 5,724,743 to Jackson.

In the system of FIGS. 7 to 9, at least one active head contains gravitysensors to measure camber and pitch of the head. Since the imaging ofthe target mounted on the opposite active head allows the system toobtain a three-dimensional (3D) spatial relationship measurement betweenthe two active heads, only one active head is required to have gravitysensors. Otherwise, the structure, operation and computations aregenerally similar to those of the earlier examples.

In the examples discussed above, the active heads have been associatedwith the rear wheels, and the targets have been associated with thefront wheels of the vehicle. However, those skilled in the art willunderstand that there are many variations of the basic configurationsdiscussed above. Also, there are a variety of different combinations ofimaging sensors with other sensors for determining the spatialrelationship that may be used. Several are described and shown below.

FIG. 10, for example, shows an arrangement similar to that of FIG. 1 inwhich the active heads and the target heads are reversed. The wheelalignment system of FIG. 10 includes a pair of passive heads 221 and 223mounted on respective wheels 222 and 224 of the vehicle 220, which arerear wheels in this example. The active sensing heads 225 and 227 areadapted for mounting in association with the respective front wheels 226and 228 of the vehicle 220. Again, each active sensing head includes animage sensor 229 or 231 for producing image data, which is expected toinclude an image of a passive target when the various heads are mountedto the respective wheels of the vehicle. In this example, the imagesensors 229 and 231 in the active sensing heads 225 and 227 are twodimensional (2D) imaging devices, e.g. cameras similar to the trackcameras in the earlier examples.

The heads 221 and 223 are passive in that they include targets of a typethat may be observed by one of the image sensors in the active heads 225and 227, but they do not include any sensing elements. Typically, thetargets comprise light and dark regions that can be detected whenilluminated by other sources and imaged by cameras or the like in theactive sensing heads 225 and 227.

As in the earlier examples, the system also includes a spatialrelationship sensor associated with at least one of the active sensingheads 225 or 227. The spatial relationship sensor enables measurement ofthe spatial relationship between the active sensing heads 225 and 227when the active sensing heads are mounted on wheels of the vehicle. Inthis example, the system uses two conventional (1D) angle sensors 333and 335 to measure the relative angles of the active sensing heads 225and 227, in the toe plane. The active heads 225 and 227 also containgravity sensors or the like to measure tilt, typically camber and pitch,of the head. Hence, the head 225 includes one or more tilt sensors 337;and the head 227 includes one or more tilt sensor 339.

As shown in the earlier examples (e.g. FIG. 2), the system also includesa computer. The computer processes image data relating to observation ofthe targets and tilt data, from the active sensing heads. The computeralso processes spatial relationship data from the at least one spatialrelationship sensor. The data processing enables computation of at leastone measurement of the vehicle.

As noted, this example is essentially a front-to-rear reversal of thetarget/active sensing head positions from that of the example of FIG. 1.Although not all variants are shown, those skilled in the art willunderstand that similar types of front-to-rear variants and/orleft-to-right variants can also be implemented for every otheralternative arrangement discussed herein.

FIG. 11 illustrates another alternative arrangement. In this example,two active sensing heads are mounted on one side of the vehicle, and twopassive sensors are mounted on the opposite side of the vehicle. Asshown, the mounting of the targets on the passive heads provides anextension out away from the wheels, somewhat, so as to allow the imagesensors in the active heads to see and image the targets. Each activehead contains an image sensor that obtains images of a target attachedto the corresponding wheel on the opposite side of the vehicle. As inthe earlier examples, each active head contains gravity sensors tomeasure camber and pitch of the head. Here, the spatial relationships ofthe two active heads are determined by two conventional angle sensorsmeasuring the toe plane angles between the two heads. Since thestructure, operation and computations are generally similar to those ofthe earlier examples, those skilled in the art should understand theexample of FIG. 11 without a more detailed discussion here.

FIG. 12 illustrates another alternative arrangement. In this example,two active sensors are mounted on one side of the vehicle, and twopassive sensors are mounted on the other side of the vehicle. Eachactive head contains image sensors that obtain images of targetsattached to the corresponding wheel on the opposite side of the vehicle.Here, the spatial relationships of the two active heads are determinedby one or more image sensors that obtain images of a target mounted onthe opposite active head. In the example, the front active head includesa target, and the rear active head includes a 2D imaging sensor forobtaining images of that target, in a manner analogous to the 3D spatialrelationship measurement in the example of FIGS. 7 to 9. At least oneactive head contains gravity sensors to measure camber and pitch of thehead. Since this system obtains a 3D position and orientationmeasurement between the two active heads, only one active heads isrequired to have gravity sensors. Again, since the structure, operationand computations are generally similar to those of earlier examples,those skilled in the art should understand the example of FIG. 12without a more detailed discussion here.

FIG. 13 is yet another alternative arrangement. This example uses afirst active sensing head containing a single 2D image sensor forobtaining images of a passive target on a first passive head mounted onthe other wheel on the same side of the vehicle. The first passive headis mounted to a wheel on the same side of the vehicle as the firstactive head. In the specific example shown in the drawing, the firstactive head is mounted on the left rear wheel, and the first passivehead is mounted on the left front wheel. One target on the first passivehead is available for imaging by the 2D image sensor associated with theleft rear wheel, that is to say, along the vehicle track on that side ofthe vehicle.

However, the first passive head also contains a second passive target ina known relative position with respect to its first passive target. Thesecond passive target is extended in front of the wheel so that it canbe viewed by a corresponding 2D image sensor on the opposite side of thevehicle, for imaging in a spatial relationship measurement. Hence, thesecond active head is mounted across from the first passive head, thatis to say on the right front wheel in the illustrated arrangement. Thesecond active head contains two 2D image sensors. One of these sensorsobtains images of the target mounted on the first passive head, attachedto the opposite (left front) wheel for the spatial relationshipmeasurement. The other 2D image sensor in the second active head obtainsimages of the target mounted on a second passive head, which is mountedon the same side of the vehicle, that is to say, on the right rear wheelin this example. The second passive head contains a single target, andthat head is mounted across from the first active head.

In the arrangement of FIG. 13, at least one of the active heads containsgravity sensors to measure camber and pitch of the head. Since thesystem obtains a 3D position and orientation measurement between the twoactive heads, only one active heads is required to have gravity sensors.In general, the details of implementation and operation of the system ofFIG. 13 should be apparent from this summary discussion and the earlierdetailed disclosure of the examples of FIGS. 1-9.

The example illustrated in FIG. 14 is generally, similar to the exampleof FIG. 13, except that in the system of FIG. 14, the first active headalso contains a second image sensor. The second image sensor in thathead obtains an image of a second target attached to the second passivehead. This configuration has an advantage over the arrangement of FIG.13 in that it only requires two unique head hardware configurationsrather that four. Both active heads are the same, and both passive headsare the same. Each of the active heads would be similar to the head 55′shown in FIGS. 8 and 9. One active head should be identified as a fronthead and the other as a rear head. This can generally be done withfirmware in the embedded processors.

A second advantage of this configuration (FIG. 14) is that the secondspatial relationship measurement is redundant information that is notrequired to calculate wheel alignment. This redundant information can beused as a calibration check on the system. If both active heads containsgravity sensors, both camber and toe can be validated. If only oneactive head contains gravity sensors, only the toe calibration can bevalidated.

In the example shown in FIG. 15, the system uses passive heads withtargets that are mounted on each of the front wheels, essentially as inthe examples of FIGS. 1-9. Active heads, shown on the rear wheels,contain 2D image sensors. A reference bar with a target on each end isplaced such that each active head can view one of the targets on thereference bar as well as the target on the front wheel of the same sideof the vehicle. The relative positions and orientations of the twotargets on the reference bar are known. The system can find the spatialrelationship of the two active heads from the measured 3D positions andorientations of the two reference targets by the active heads and theknown relationship of the two reference targets. This provides thespatial relationship information obtained by the spatial relationshipsensor—target of the example of FIGS. 7 to 9. Since the referencetargets are fixed in position they can also be used as a reference formeasurements during rolling runout. Those skilled in the art shouldappreciate the detailed structure and operations of this example, fromthe drawing, this description and the earlier discussion of othersimilar examples.

The example illustrated in FIG. 16 generally works just like the exampleof FIG. 15, except there is only a single reference target. The viewingangle of the image sensors in the active heads must be wide enough to beable to view both the passive head target on the same side of thevehicle and the single reference target.

FIG. 17 illustrates yet another example of a hybrid wheel alignmentsystem. Here, the system uses passive heads with attached targetsmounted on each front wheel. The active heads are mounted on the rearwheels, as in several of the earlier examples. Each active head containsa 2D image sensor to obtain images of the passive head target on therespective side of the vehicle.

The image sensors are extended forward from the center of the rearwheels so that the sensors are located forward of the rear wheel tires,so as to provide a cross-vehicle line of sight under the vehicle. One ofthe image sensors, in the example the sensor on the active head mountedon the left rear wheel, contains a partial mirror that passes imagesfrom the passive target or reflects images from a target mounted on thecorresponding active head on the other side of the vehicle. Theoperations of the mirror are shown in more detail in FIG. 18.

Light from the passive target on the passive head mounted on the sameside of the vehicle, that is to say, on the left front wheel in theillustrated arrangement, passes directly through the half-silveredmirror to the 2D image sensor on the active sensing head mounted on theleft rear wheel. Light from the passive target on the opposite activehead, that is to say on the active head mounted on the right rear wheelin the illustrated arrangement, arrives at an angle to the partiallyreflective side of the mirror and is reflected into the 2D image sensoron the active sensing head mounted on the left rear wheel. The advantageof this system is that it eliminates one image sensor by allowing one ofthe sensors to view two different targets.

While the foregoing has described what are considered to be the bestmode and/or other examples, it is understood that various modificationsmay be made therein and that the subject matter disclosed herein may beimplemented in various forms and examples, and that the teachings may beapplied in numerous applications, only some of which have been describedherein. It is intended by the following claims to claim any and allapplications, modifications and variations that fall within the truescope of the present teachings.

1. A wheel alignment system, comprising: a pair of passive heads, each comprising a target, for mounting in association with a first pair of wheels of a vehicle that is to be measured by operation of the wheel alignment system; a pair of active sensing heads for mounting in association with a second pair wheels of the vehicle, each respective one of the active sensing heads comprising an image sensor for producing image data including a representation of an image of one of the targets; a spatial relationship sensor associated with at least one of the active sensing heads, for measuring a relationship between the active sensing heads, when the active sensing heads are mounted on wheels of the vehicle; and a computer for processing image data relating to observation of the targets and relationship data from the spatial relationship sensor, to compute at least one measurement of the vehicle. 2-20. (canceled) 